The present invention relates generally to the field of telecommunications, and more specifically, to the field of automatic gain control circuits for cellular telephones.
Automatic gain control (AGC) circuits are well known in both analog cellular telephones and digital cellular telephones, including code division multiple access (CDMA) cellular telephones. It is often necessary to vary the amount of gain applied to signals received at the cellular telephone for proper analysis and processing of received signals. Such control of the gain of received signals is particularly important with digital communication methods. Particularly with CDMA systems, it is also well known to control the strength of signals transmitted from a cellular telephone in response to the strength of signals received by the cellular telephone. As received signal strengths increase, indicating closer proximity to a base station, transmission strengths are correspondingly lowered in view of the closer proximity. With closed loop systems, cellular telephones are responsive to commands received From a base station to raise or lower transmitted signal levels.
One common AGC method includes measuring a received signal level and comparing the received signal level to a reference level to control the gain applied to both receive and transmit portions of a cellular telephone. U.S. Pat. No. 5,107,225, issued to Wheatley, III et al, describes a cellular telephone which includes nonlinearly compensated adjustable amplifiers which are controlled in response to an integrator comparison between a reference signal and a received signal strength indication generated by a logarithmic detection device which receives signals before baseband demodulation. Although said to be capable of exhibiting rapid, high dynamic range signal power control, that device embodies a rather complex, expensive, and rigid method of providing a cellular telephone AGC function. There is, therefore, a need in the industry for an AGC circuit which addresses these and other related, and unrelated, problems.